1. Field of the Invention
The present invention relates generally to a cross member for a motor vehicle frame. More particularly, the present invention relates to a cross member having passages therein to permit the passage therethrough of rack and pinion steering linkage.
2. Disclosure Information
Motor vehicle frames having longitudinally extending frame rails interconnected with transverse cross members are well known in the motor vehicle industry. The forward portion of the longitudinal frame rails are often designed to absorb energy by plastically collapsing under certain impacts. One factor that determines the energy absorbing character of the motor vehicle is the "free length" of the frame rail. Specifically, this relates to the length of frame extending forward from the forward face of the front cross member.
As is well known, the front cross member serves multiple roles. First, unlike a unibody vehicle, cross-members are interspersed between the longitudinal rails to provide torsional rigidity to the overall frame structure. Second, the front cross member is commonly situated under the front of the engine to provide strength for mounting the engine. Third, the front cross member provides support for the front suspension attachments. The suspension imparts lateral loads on the frame that are best resisted by a transverse cross member.
Recently, another variable has entered the equation for the design of the front end of some vehicles, especially those in the sport utility market segment. Consumers are demanding vehicles with a minimum "overhang." Overhang is one measure of a vehicle's ability to traverse a path having a dramatic change in slope, such as a climbing a steep hill, or entering a steeply inclined driveway. The vehicle with shorter overhang is less likely to drag the front end on the ground. The significant component of vehicle overhang under consideration here is the distance from the front axle centerline to the leading edge of the vehicle, typically the bumper. Therefore, it can be seen that overhang is minimized by locating the front axle as far forward as possible. Since the front cross member is typically mounted just forward of the front axle, the desire to minimize overhang conflicts with the desire to provide maximum "free length" of the frame for absorbing energy.
This conflict has been a significant impediment to incorporating a rack and pinion steering gear assembly into such vehicles. It is commonly known to those skilled in the art to locate the rack and pinion steering gear assembly center line as close to the front axle centerline as possible. Typically this has been accomplished by mounting the rack and pinion gear assembly on the front or the rear face of the front cross member. Unfortunately, the rack and pinion steering gear assembly is as effective as the cross member for purposes of compromising free length. As a result, these locations consume precious free length otherwise required for energy absorption.
One solution has been to locate the rack and pinion steering gear assembly directly beneath the cross member. However, this design significantly compromises ground clearance. The unresolved conflicts created by these design objectives has prevented the incorporation of rack and pinion steering in vehicles of the body on frame design. Instead, as shown in FIG. 1, a recirculating ball steering gear with the associated linkage, has been used, much to the dissatisfaction of many consumers who prefer the tight, crisp steering that is associated with rack and pinion steering assemblies.
Therefore, it would be advantageous to provide a front cross member capable of cradling a rack and pinion steering gear assembly and providing the strength necessary to support the engine and suspension imposed loads, while providing sufficient free length, overhang and ground clearance.